1. Field of the Invention
The present invention relates to a safety binding for a cross-country ski. More particularly, the invention relates to a binding of the type comprising a longitudinal rib bordered laterally, respectively, on both sides, by two approximately planar and coplanar longitudinal surfaces with respect to which the rib forms a projection. The rib is adapted to engage an elongated groove in a sole of a shoe or boot in a position such that two elongated surfaces bordering the groove face the longitudinal surfaces. In addition, an apparatus is mounted on the rib which defines an axis of rotation around which an anterior zone of the shoe sole is adapted to pivot with respect to the rib. This axis is transverse and parallel to the longitudinal surfaces.
2. Description of Pertinent Information
Traditionally, cross-country ski bindings of the type mentioned above position the rib and the two longitudinal surfaces on a plate attached to the ski. The plate serves as an intermediate support of the shoe on the ski. Furthermore, the plate comprises means for defining the transverse axis of rotation of the anterior zone of the sole of the shoe with respect to the rib.
Normally, the plate is integrally attached to the ski in a permanent fashion, for example, by means of screws. As a result of this structure, during a twisting or torsional fall the torsional moment generated by this fall is communicated to the leg of the skier by the engagement of the groove in the sole and the rib, thereby causing an excessive moment to be applied to the leg of the skier which causes the leg to break. To minimize this risk, it has been proposed, for example in West German patent application No. 33 10739, to use a plate which can be immobilized and which can also laterally pivot with respect to the ski as soon as the sole applies a lateral force to the rib of an intensity which exceeds a predetermined threshold release value which is selected to avoid any risk of breaking the leg, thereby permitting lateral pivoting of the means for defining the axis of rotation of the anterior zone of the sole of the boot with respect to the rib.
The plate described in the West German patent marks considerable progress in the safety of such cross-country bindings. However, this plate has a certain number of disadvantages. First, the movable elements comprising the plate and the means for defining the transverse rotation axis of the anterior zone of the sole of the shoe with respect to the rib have a cumbersomeness and a mass which are not negligible. This occurs because the mechanical resistance requirements of the plate impose a certain thickness on the plate under the rib and, more importantly, under the lateral surfaces bordering the rib, in comparison with plates that are integral with the ski and which do not laterally pivot.
Second, the use of the techniques set forth in the German patent result in a substantial increase in the mass of the ski binding assembly, which adversely affects the dynamics of the ski. Furthermore, the inertia of the mobile ski binding assembly, resulting from the relatively substantial mass of the assembly, causes a certain sluggishness in the lateral release of the assembly in response to a lateral force on the binding. In addition, after lateral release there is a danger that the leg of the skier may be wounded due to the shock of the leg of the skier against a lateral projection which extends transversely to the plate.
The sluggishness of the lateral release can be partially compensated for by the interposition of a bearing or slide means between the plate and the ski. However, the use of such a compensation means has another disadvantage, namely, that of spacing the shoe further away from the ski due to the thickening of the plate particularly under the longitudinal surfaces bordering the rib. This increase in the spacing between the shoe and the ski reduces the aerodynamics of the boot-ski assembly and adversely affects the stability of the skier.
Thus, there is a need for a cross-country ski binding that will permit lateral pivoting of the rib and shoe or boot which does not increase the cumbersomeness or mass of the binding, which does not cause any sluggishness in the lateral release of the boot when excessive torsional forces are present, which reduces the danger that the skier will wound his foot on a lateral projection, and which maintains the foot of the skier close to the top surface of the ski.